The bull elephant yard actually housed a lone hippo long ago when Cleopatra was still alive. In actuality, she occupied a yard half the size of the current bull yard, and was just fine in the tiny pool, relatively speaking. By relatively, I mean she lived a long life and didn't get maimed or killed by any conspecifics. She actually was reputed to be very tolerant of her neighbor Gretchen, an older female African elephant.
Problem is, there isn't any indoor holding for hippos in the current elephant house. All of the water basin areas were filled in and built over to make more room for the elephants.
A lot of movement should be forthcoming with the elephants eventually leaving for their new exhibit in a year or 2. Then the giraffes into the elephant building. Hoofed stock has largely been shipped out in the Africa main yard.
The zoo rarely surprises me in a pleasant way these days, but it would be nice to see them use some of that space in Africa for a more appropriate hippo holding. It does nothing for the current problem, and more immediate action likely needs to be taken. My point is, if you're going to empty out your exhibits in Africa, then you might as well use the space for a species that's poorly housed. It would totally botch the East African theme that was originally intended, but I wouldn't be mad if Africa eventually housed hippos, okapis and bongos in some configuration. Zoogeographic themes are largely arrangements of convenience in Cincinnati with respect to recent history, so it wouldn't really hurt anything.